Author

Date of Award

1983

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

The polypeptide composition of purified radioactively labeled equine infectious anemia virus (EIAV) was investigated using high-resolution sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and guanidine hydrochloride gel filtration (GHCl-GF) to catalog key biochemical properties including molecular weights, stoichiometry, isoelectric points and modifications (glycosylation or phosphorylation). The results of these studies indicate that EIAV contains four major nonglycosylated proteins (p26, pp15, p11, and p9) and two glycoproteins (gp90 and gp45), which together account for greater than 95% of the total virion protein. Four minor polypeptides (p70, p61, p30, and p23) of unknown significance were also detected reproducibly. Comparisons of the major purified proteins by peptide mapping procedures demonstrated the unrelatedness of the proteins, including two glycoproteins, gp90 and gp45. Localization experiments indicated that gp90 and gp45 constitute the envelope glycoproteins while nonglycosylated polypeptides (p26, pp15, p11 and p9) constitute the internal components of the virus. EIAV p11 is closely associated with the viral genome in a ribonucleoprotein complex and pp15 seems to be a component of inner coat while p26 and p9 appear to comprise the icosahedral core shell. Thus, our results demonstrated that EIAV, a putative lentivirus, contains polypeptides analogous to the structural polypeptides of prototype-C oncornaviruses (Montelaro and Bolognesi, 1980). The recurrent nature of equine infectious anemia (EIA) has been attributed to relatively rapid antigenic variations in EIAV during persistent infection under selective immune pressures. This model was tested by biochemical analyses of five serologically distinct EIAV isolates, recovered from experimentally inoculated ponies (Orrego, 1983). Comparative SDS-PAGE analysis of proteins and two-dimensional peptide mapping of their tryptic digests revealed that gp90 and gp45 undergo structural alterations during virus replication. No differences were found in the internal antigens after virus replicated in a single animal; however, EIAV p26 did indicate a few structural variations when the virus was passaged into another animal. Thus, serological differences among EIAV isolates are correlated to the structural variations in the polypeptides of EIAV. The capacity to alter antigenic structure, especially envelope glycoproteins, may represent an important mechanism for retroviral persistence in the presence of immune response by the host.